Simple lateral flow immunoassay devices have been developed and commercialised for detection of analytes in fluid samples, see for example EP291194. Such devices typically comprise a porous carrier comprising a dried mobilisable labelled binding reagent capable of binding to the analyte in question, and an immobilised binding reagent also capable of binding to the analyte provided at a detection zone downstream from the labelled binding reagent. Detection of the immobilised labelled binding reagent at the detection zone provides an indication of the presence of analyte in the sample.
Alternatively, when the analyte of interest is a hapten, the immunoassay device may employ a competition reaction wherein a labelled analyte or analyte analogue competes with analyte present in the sample for an immobilised binding reagent at a detection zone. Alternatively the assay device may employ an inhibition reaction whereby an immobilised analyte or analyte analogue is provided a detection zone, the assay device comprising a mobilisable labelled binding reagent for the analyte.
An assay device may determine more than one analyte. For example in the case of assays for the determining the presence of drugs of abuse, the device may be capable of determining a whole panel of drugs. Such lateral flow immunoassay devices are provided with multiple detection zones, such zones being provided on a single or multiple lateral flow carriers.
Determination of the result of the assay has been traditionally carried out by eye. However such devices require the result to be interpreted by the user which introduces an undesirable degree of subjectivity.
As such, digital devices have been developed comprising an optical detection means arranged to determine the result of the assay as well as a display means to display the result of the assay. Digital assay readers for use in combination with assay test-strips for determining the concentration and/or amount of analyte in a fluid sample are known as are assay devices comprising an integral digital assay reader.
Light from a light source, such as a light emitting diode (LED), is shone onto a portion of the porous carrier and either reflected or transmitted light is detected by a photodetector. Typically, the reader will have more than one LED to illuminate various zones of the carrier, and a corresponding photodetector is provided for each of the plurality of LEDs. EP1484601 discloses an optical arrangement for a lateral flow test strip digital reading device comprising a baffle arrangement allowing for the possibility of reducing the number of photodetectors in the device.
Such devices are often designed to be single use and therefore it is desirable to keep the costs of such devices as low as possible, especially where expensive optical and electronic components are involved.